US2259121A

US2259121A - Radio receiver circuit

Info

Publication number: US2259121A
Application number: US295712A
Authority: US
Inventors: Lemuel M Temple
Original assignee: Individual
Current assignee: Individual
Priority date: 1939-09-20
Filing date: 1939-09-20
Publication date: 1941-10-14
Anticipated expiration: 1958-10-14

Description

Oct 14, 1941. l.; M. TEMPLE RADIO RECEIVER CIRCUIT Filed Sept. 20, 1959 100 11a 120 1.50 70 wwf/75W mfr/m5 INVENTOR email M Tenga/e BY wwfm ATTORNEY Patented Oct. 14, 1941 UNITED STATES PATENT GFFICE RADIO RECEIVER CIRCUIT v l Lemuel M. Temple, Scarsdale, N. Y.

Application September 20, 1939, SerialNo.l295,712

i (C1. 17a-e171) 4 Claims.

invention relates to radio receivers and more particularly to receivers operated with a high voltage dry battery commonly known as a B battery.

The principal feature of my invention is the provision of means in the output circuit of the receiver to reduce the B battery current used by the output tube and thereby markedly extend the useful life of the B battery with consequentreduction in renewal battery and operation cost.

My invention is based upon observations of the fact that'many radio receivers are operated by theirownrs at a substantially'lower power output level, that is, so called volume or listening level, than that for which the receiver is designed or rated; and a realization of how the receiver output may be controlled in accordance with this practice and effect marked economy in the life of the B battery.

Thel usual battery type receivers are designed to give a power output of about 200 to 500 milliwatts with a common average of around 325 milliwatts. Many users of such receivers however maintain the output or Volume at a substantiallyy lower level, i. e. around 50-100 milliwatts. This is especially true of battery receivers used'` in the ,country `with quiet'surroundings which do not require high volume. This normal control by the user ofthe radio set, however, does not effect any economy in the operation of the B battery since the B ycurrent used is unchanged whenthe iusualclass A type amplifier is used. In laccordance with my invention I have provided in the receiver circuit means for controlling the output of the receiver to the usual reduced listening level and for reducing the B'battery current consumption proportionally. This reduction in'B battery current' used by the output tube in the receiver is as much as 5,0% of the normal consumption and may range as high as about 65%, 'The'B battery current consumption is regulated in accordance with my invention by an arrangement for overbiasing the output tube; that is, increasing the normal biasf'on a grid or grids v4'i'zof'tlieoutput tube so as to reduce the plate current drawn by that tube. The device embodying my invention also includes 'means whereby the over-biasing of the output tube may be manually reduced and the biasing of this tube returned to a value for maximum performance.

By this arrangement if the voltagt of the B Y battery vhas dropped materially so that the set noflonger is giving satisfactory performance, the reduction of the bias on the control grid of the output tube has the effect of permitting a greater amount of current to flow from the B battery and satisfactory performance of the set can thereby be restored for an additional period, which will be valuable, even though the drain on the B .battery during this period will be very heavy. I

,The means for effecting this overbiasing may bel in-the form of 'an added resistance in the plate control-grid circuit, or taps on the `B battery with a variable connector to utilize varying amounts of voltage" from this battery applied to the screen grid of the output tube, or a combination of these two means. The added grid biasing resistor is the preferred arrangement from the standpoint of simplicity of construction and operation. A switch is also provided for electrically disconnecting this over-biasing resistor from the grid circuit, when the current supply from the B battery has been reduced, by use of the battery, to a point where further limiting the current would adversely-affect the operation of the receiver, that is, reduce the power output to an undesirably low listening level.

vThe cost of power from dry batteries is very high in comparison with metered power and a saving of battery current consumption is vital to the economically successful use of dry battery receivers. Furthermore, the B current used by the output tube or tubes is large compared with the other tubes in the set, and generally constitutes from about one-third to one-half; of the total current consumption. Accordingly I have incorporated my B battery current saving arrangement in the circuit of'the output tube.

' It is to be noted that the useable life of a B battery is seldom determined Vsolely by the decline of battery voltage toa point where there isinsuicient voltage to operate the tubes of a receiver. Normally the life lof aB battery is determined by the decline of Vreceiver performance such as sensitivity-ofv the receiver, audio frequency distortion, andvloss of power output at the loud speaker. I'hese factors effectively determine the B battery lifeI because they determine the receiver performance and when this becomes unsatisfactoryto the listener the B batteries are discarded and replaced by new batteries. Nevertheless, the discarded B batteries `have not delivered "their full"` power, but have become unsatisfaztorydue to the loss of B voltage. Because of this declining Bvoltage and because oflvariations in the operation of the receiver dueto different locations of the receiver with respect to the transmitting station, satisfactory V57;'Theeilectfnof. electrically resista I5, iaihisefgii IgA-Pereda@ .the amount 75- operation is most effectively obtained by the use of a self-biasing output tube circuit. Such a circuit provides automatic adjustment of the bias voltages on the tubes during the decline of the B battery. The B battery current controlling 5 means of my invention is therefore preferably used in a self-biasing output tube circuit. Also the switch means which I employ enables the B battery current reducing means to be eliminated electrically from the circuit when the B battery 10 has declined through use to an unsatisfactorily low level. At this point the switch may be employed to return the output circuit to its normal self-bias condition, and thereby eiectively increase the current supplied from the B`battery .15 during the remainder of its use vin the circuit. In the usual case, my current savingv arrange# ment may be employed for abouti the rstlialf 'oi the life of the B battery.

The novel features and details of my'invention 20 will be further understood by reference tothe accompanying drawing, in which: l

Y Figure l is' a'circuiti-diagram `showing the adaptation ko'fmy invention in the output circuit of a'battery operatedradio receiver; and j i Figure 2 isa graph showing the difference in'B battery current consumption and life with'the usual self-bias battery .receiver and the same type of "receiver utilizing the current reducingy means of'myinvention. f Y 1A; 30 Referring now to Figure l vthe circuit-shown therein is an output circuit of aconventionalA type Y receiver :having one pentode tube as the output tube. i It is to be understood, however, that two or more'outputtubes may be used if desired; a 35 common ,example being two; output tubes -connected in pushpull arrangement.' For the sake of simplicity, only' the last output stage has been illustrated` in this figure, and legends givenon the drawing to indicate the conventional connec- 40 tions of thiszoutput` circuit with the preceding portion of the radio circuit, e. g. detector or amplierV circuit. p 1

The output Vcircuit shown in Figure 1 comprises,- generally, a Vpentod'e output tube IIJ, an output 45 transformer] I, and loud speaker I2, a B battery I :3,"two biasing resistors I4 and I5, and a switch It. Aresistorvlland condenser I8 are provided for connecting-the output tube to the detector or audio driver.v rlhe `other ,connectorsl are indi- 50 catedonthe drawing. The B battery I3 supplies positive 'voltage to the plate I9, and screen grid `20 and negative voltage to kthe controlgrid 2|. The voltage applied to the nlament 2v2 issupplied fromthe Apbattery, notshown, but indicated. V55 The normal;- grid biasing-.voltage applied to -the control grid 2| inthe selig-biasing;arrangement shown in thisffigure;Y is controlledby the grid resistor I 4,,and in theconventionaloperationiof this: circuit only this resistor isusedfto regulate 60 the grid bias. A ,v f Now tooperate-lthe above `describedcircuit in (accordancet with my invention and thereby conserve` the vB battery current,an additional grid resistor I5, shovvn in Figure 1,.is electricallyconfv 65 nected inthe grid biasing lcircuit byppening the switch I6; it: isp-to be noted that when this switch is closed'thatthe resisto-n I 5 will be shunted and Y the current will vfollow.thezpath of least resistanceV around v`this resistor andv` throughV the switch. I6. 7o However,V when 4the. switch IB is open icurrent iiows directly through this circuit including additional resistor I5. Y Y I t ding the'aaditionm of plate current drawn by the output tube I0. Because of the fact that the additional resistor I5 effects the increase in the negative bias applied to the control grid 2 I, the bias grid 2| controls the amount of plate current in the usual manner. More specically, current from the battery I3 flowing through the resistance I5 will produce a voltage drop across that resistance which will be added to the voltage drop produced normally across the self-biasing. resistor I4 and the combined voltage drops willbe applied to the control grid 2| and increase the bias thereon in .Y vproportion to the value of the added resistance I5, and current through them.

lTo assume a specic example for the sake of Y illustration, the B battery I3 may supply 90 volts and the vrequired D. C. voltage for the grid 2| is .41/2'vo1tsand`the total B battery current required by all of the tubes in the set is l2 milliamperes. Under this set of conditions the value of the resistance I5would be 375 ohms as determined in the usual way from the application of Ohms law,

E Rw Itis thus seen that the value of the additional biasing resistor I5 is determined by the amount of B current reduction desired which places a greater than normal'negative biasing voltage on the control grid 2| ofthe output tube I0. Such an increase in bias voltage reduces the plate current oir-the voutput tube., Also the plate and screen currents of all ofthe other tubes in thev circuit are reduced by the difference in voltage drop across the-resistance I5 andthe lvoltage drop across the combined resistors I4 and I5in series. This combined voltage drop is subtracted from the total B voltage of the battery I3. l

The two resistors I4 and I5 have been shown in Figure l as two separate resistors, but it is to be understood that a single resistance with conventional tap might be used. Also the resistors I4 and I5 may be made variable if desired.

As above indicated the switch I6 will permit the user of the radio set to have full volume from the vreceiver with vthe usual B battery current Y consumption; or reduced volume and reduced battery current with resulting longer B battery life. The switch I5 maybe located on the front panel of the radio set and may be in the form of a simple toggle type of switch-with an ori-and-oi position. One of the positions may be labeled, if desired, feconomy position which indicates that the resistance I5V is-in circuit and the'B battery current reduced.

' YAsindicated in Figure lan `alternative or combined means of extending the life of the B battery I3 comprises the use of taps 23 and a switch connector 24. By connecting thel member 24 to different ones of the taps 23, the B battery volt-f age applied to thescreen grid 20 may be varied. That is, the voltage on thescreen grid 20 may be decreased to effect a decrease in the amount of plate current drawn by the plate I9. The switch meansld may be connectedindependently or may be connectedin tandemwithjthe switching means I I5v so -rthat the eifects'may be applied singlyor in combination.' k Referring now kto VFigure 2, the curve 25 illustrates 1 the B battery current, in milliarmperes, consumed by the entire receiver when the output circuit of the receiver is operated in the vconven tional manner, that is, withV normal bias on Athe grid'of,` the output tube. An examplerof such operation would be that talging place in the cir-l cuit of Figure 1 when the resistor i5 was not in use. This curve shows that the B battery current used varies between about 10 to 25 milliarnperes during the normal useful life of the B battery, that is, where it has a Voltage supply of about 130 Volts down to about 70 volts, when it is discarded.

Curve 2S illustrates the B battery current consumed when the circuit is operated in accordance with my invention, that is, when the over-bias resistor l is utilized. As shown by this curve the B battery current varies between about 7 to 15 milliamperes which constitutes a substantial reduction over the above normal operation.

The

curves

21 and 23 complement the

curves

25 and 26 and illustrate the difference in effective fe of the B battery when operated under normal bias (curve 21) and when operated with over bias (curve 28), the latter being in accordance with my invention. As shown by these two curves the normal life of the B battery is increased from about SGO hours to about 120) hours when using the over-bias feature of my invention.

I claim:

1. In a battery operated radio receiver having a plurality of tubes having screen grids, a ccrnmon source of B voltage for a plurality of said tubes including the output tube, biasing means for controlling the potential of the control grid of the output tube, such biasing means utilizing a portion of said B voltage determined by a resista-nce in the common negative B return to the tube filaments, means for applying a positive potential to the screen grids of said plurality of tubes from said source of B Voltage and means for manually reducing such resistance by a predetermined value whereby the control grid potential of the output tube may be reduced and the B current thereby may be immediately greatly increased in the output tube and at the same time will also be increased in the remainder of said plurality of tubes.

2. A radio receiver as dened in claim l, in which the means for reducing such resistance comprises a manually operable switch for bypassing a portion of such resistance.

3. A radio receiver as dened in claim 1 which further includes a variable connector on the B battery for varying the amount of voltage supplied by said battery to a grid of said output tube.

4. In a battery operated radio receiver having a plurality of tubes having screen grids, a com- Vmon source of B Voltage for a plurality of said tubes including the output tube, biasing means for controlling the potential of the control grid of the output tube, such biasing means utilizing a portion or" said B Voltage determined by a re sistance in the common negative B return to the tube iilaments, means for applying a positive potential to the screen grids of said plurality of tubes from said source of B voltage, means for ianually reducing such resistance by a predetermined value comprising a switch for by-passinCr a portion of said resistance whereby the control grid potential of the output tube may be reduced and the B current thereby may be irnmediately greatly increased in the output tube, a variable connector on the B battery for varying the amount of voltage applied by said battery to a grid of said output tube and common means for varying said connector and operating said switch whereby said resistance may be decreased and the amount of B voltage increased simultaneously.

LEMUEL M. TEMPLE.